Recently, there is proposed a system in which an in-vehicle unit mounted on each of a plurality of vehicles (referred to as host vehicles) wirelessly communicates with other in-vehicle units existing within a predetermined range from the in-vehicle unit itself without using a wide area communication network. This type of communication between in-vehicle units is generally referred to as an inter-vehicle communication.
This type of in-vehicle unit includes a positioning radio wave receiver and a sensor. The positioning radio wave receiver such as a GPS receiver receives a radio wave from a positioning satellite to specify a current position of the in-vehicle unit itself. The sensor, namely an acceleration sensor or a gyro sensor, detects a predetermined physical state quantity such as an acceleration or a rotational angular speed. A detection result from the acceleration sensor or the gyro sensor is used to correct a current position specified by the positioning radio wave receiver. The in-vehicle unit may include a sensor to detect a physical state quantity such as illuminance and temperature in addition to an acceleration or a rotational angular speed.
The in-vehicle unit transmits information about the in-vehicle unit itself such as a current position and an acceleration of the in-vehicle unit itself to a service provider terminal (e.g., a roadside instrument) that provides the in-vehicle unit with a predetermined service. The in-vehicle unit can thereby obtain a service provided by the service provider terminal. For example, the in-vehicle unit provides the service provider terminal with current position information and can thereby obtain a service associated with the current position.
Patent literature 1 discloses the technology that settles a predetermined threshold value as an operation range of an acceleration sensor and uses the threshold value to diagnose whether the acceleration sensor operates normally.